Controlled capacity torque converter clutch lock-up transition control

Abstract

A torque converter clutch control provides for a controlled capacity mode of operation wherein clutch slip is controlled to a reference value. A lock mode is also provided wherein clutch slip is eliminated. The transition from the controlled capacity mode to the lock mode is caused to occur when clutch slip is stabilized by increasing clutch engagement force by an amount sufficient to smoothly reduce slip speed to zero and thereafter maintain zero slip. The increase in engagement force is marginally sufficient to maintain slip at zero thereby allowing engine torque excursions to be absorbed by allowing slip during such excursions. Transitions back to the controlled capacity mode are adapted to current torque and slip conditions.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. In a motor vehicle including a torque converter adapted to receive engine torque through an input member thereof and to supply torque to the vehicle drivetrain through an output member thereof, a clutch mechanism connected between the input and output members of said torque converter, the clutch mechanism being operative when fully engaged in a lock mode to prevent slip between such input and output members to thereby provide torque capacity at least as great as the engine torque, and when less than fully engaged in a controlled capacity mode to permit slip between such input and output members to thereby provide torque capacity less than the engine torque, and a clutch actuating mechanism for controlling the torque capacity of said clutch according to the net fluid pressure in a control chamber thereof, a method of operating said clutch mechanism so as to avoid perceptible transitions between the lock and controlled capacity modes, comprising the steps of: during controlled capacity mode operation, varying the net fluid pressure in said control chamber in response to torque converter slip deviation from a reference slip;   at the onset of lock mode operation from controlled capacity mode operation, suspending further variance of the net fluid pressure in response to torque converter slip deviation from the reference slip and adding thereto a predetermined lock mode fluid pressure step to establish an initial net fluid pressure in the lock mode; and,   at the onset of controlled capacity mode operation from said lock mode operation, reducing the net fluid pressure by the lock mode fluid pressure step to establish an initial net fluid pressure in the controlled capacity mode.   
     
     
       2. A method as set forth in claim 1, including the step of: initiating the controlled capacity mode of operation from the lock mode of operation when torque converter slip exceeds a predetermined lock mode termination slip threshold, and when so initiated foregoing the reduction of the net fluid pressure by the lock mode fluid pressure step when establishing the initial net fluid pressure in the controlled capacity mode.   
     
     
       3. A method as set forth in claim 2, including the step of: delaying initiation of lock mode operation from controlled capacity mode operation for a predetermined minimum duration where controlled capacity mode operation was initiated due to torque converter slip exceeding said predetermined lock mode termination slip threshold.   
     
     
       4. A method as set forth in claim 1, including the step of: during lock mode operation varying said net fluid pressure as a function of engine output torque.   
     
     
       5. A method as set forth in claim 1 wherein the predetermined lock mode fluid pressure step is marginally sufficient to eliminate torque converter slip thereby causing transition into lock mode at a net fluid pressure which will permit slip between the input and output members during relatively large engine torque perturbations. 
     
     
       6. A method as set forth in claim 1, including the step of: initiating the lock mode of operation from the controlled capacity mode of operation when torque converter slip remains below a predetermined lock mode initiation slip threshold for a predetermined duration.   
     
     
       7. In a motor vehicle including a torque converter adapted to receive engine torque through an input member thereof and to supply torque to the vehicle drivetrain through an output member thereof, a clutch mechanism connected between the input and output members of said torque converter, the clutch mechanism being operative when fully engaged in a lock mode to prevent slip between such input and output members to thereby provide torque capacity at least as great as the engine torque, and when less than fully engaged in a controlled capacity mode to permit slip between such input and output members to thereby provide torque capacity less than the engine torque, and a clutch actuating mechanism for controlling the torque capacity of said clutch according to the net fluid pressure in a control chamber thereof, a method of operating said clutch mechanism so as to avoid perceptible transitions between the lock and controlled capacity modes, comprising the steps of: during controlled capacity mode operation, establishing the net fluid pressure in said control chamber as a summation of a baseline fluid pressure and an accumulation of fluid pressure adjustments made in response to torque converter slip deviation from a reference slip;   at the onset of lock mode operation from controlled capacity mode operation, suspending further accumulation of fluid pressure adjustments and establishing a lock mode fluid pressure offset comprising the summation of said accumulated fluid pressure adjustments and a predetermined lock mode fluid pressure step, and thereafter during lock mode operation, establishing the net fluid pressure as the summation of said baseline fluid pressure and said lock mode fluid pressure offset; and,   at the onset of controlled capacity mode operation from said lock mode operation, establishing an initial net fluid pressure in the controlled capacity mode as the summation of the baseline fluid pressure and the accumulated fluid pressure adjustments.   
     
     
       8. A method as set forth in claim 7 wherein said initial net fluid pressure at the onset of controlled capacity mode operation from said lock mode operation is established as the summation of the baseline fluid pressure and the lock mode fluid pressure offset when the onset of controlled capacity mode operation results from torque converter slip exceeding a predetermined lock mode termination slip threshold. 
     
     
       9. A method as set forth in claim 7 wherein the predetermined lock mode fluid pressure step is marginally sufficient to eliminate torque converter slip thereby causing transition into lock mode at a net fluid pressure which will permit slip between the input and output members during relatively large engine torque perturbations. 
     
     
       10. A method as set forth in claim 7 wherein said baseline fluid pressure is established as a function of engine torque.